<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <script>
        function periodIsLate(last, today, cycleLength) {
            return (today - last) / 1000 / 60 / 60 / 24 > cycleLength;
        }
    </script>
</body>
</html>